The invention relates to a control system for protecting from overloading an internal combustion engine whose output is set, with an output-determining signal, as a function of an input signal that characterizes the desired output.
German Patent 195 15 481 A1 discloses a control system, in which a desired output is specified via a selection lever. From this an engine speed target is calculated for a speed closed-loop control circuit and a helix angle target is calculated for a load-regulating step. The engine speed controller calculates from the system deviation an injected fuel quantity as well as the difference between it and the maximum possible injected fuel quantity. This difference is routed to the load-regulating step. The load-regulating step controls a regulating propeller as a function of the helix angle target, the injected-fuel quantities and the engine speed gradients. In this system, however, the output torque of the internal combustion engine is not taken into consideration. Changed boundary conditions, for example higher fuel quality or rapid increases in load at the output, bring about high engine torque values, which can be above the values specified by the engine manufacturer and cause damage to the internal combustion engine.
Based on the related art described above, the object of the present invention is to further develop a more certain protection of the internal combustion engine.
The objective is achieved according to the present invention by a control system in which a differential torque is calculated from the current engine torque and a maximum permissible engine torque. The differential torque in this situation in large part determines a second signal. The second signal and a first signal determined from the desired output are routed to a selecting means. The selecting means are used to set the first or second signal as the output-determining signal. An xe2x80x9coutput-determining signalxe2x80x9d in the sense of the invention is an injected-fuel quantity or a travel path of a control rod. In an embodiment the selecting means contain a minimum value selection. The minimum value selection is used to set the signal whose pulse value is lowest as the output-determining signal.
In an embodiment, the first signal is determined via a first controller, or alternatively, via a function block. The second signal, in turn, is determined via a second controller.
The control system of the present invention is configured such that the first signal represents the output-determining signal. The output of the internal-combustion engine is determined by the first controller or by a function block as a function of the desired output, i.e., it is in speed mode. If the torque output of the internal combustion engine exceeds the maximum permissible engine torque, the value of the second signal drops below the value of the first signal. A change in the dominance to the second controller then occurs via the selecting means. The second controller determines via the second signal the output of the internal combustion engine, i.e. it is in torque-limit-controller mode, hereinafter referred to as MBR mode. On the basis of the system deviation, the second controller reduces the output torque via the reduction of the output-determining signal until it falls below the maximum permissible engine torque . After that, a switch back to the first controller takes place.
In order to avoid erratic changes of the output-determining signals when changing dominance, the two control circuits are coupled with each other, wherein the integral-action component of the second controller is either set to the value of the first signal or limited, in dependency upon the differential torque.
The solution of the present invention and its embodiment offer the advantage that in the case of a rapidly increasing torque at the output, for example with the re-entry of a waterjet drive, there is a targeted reaction, since the output-determining signal is reduced. The internal combustion engine is effectively protected this way from overloading.
Another advantage is that the internal combustion engine is easier to tune. As is generally known, the individual parameters of the internal combustion engine, for example the limit value line (DBR curve) of the maximum permissible injected fuel quantity, are determined for each internal combustion engine in test bench trials. However, these applied data values differ from one internal combustion engine to another of the same type, and are valid only for the predetermined boundary conditions. By contrast, the invention opens the possibility of being able to use identical data values, and specifically that the maximum engine torque is delivered under all possible boundary conditions. If the measured engine torque is greater than the maximum permissible engine torque, then the second controller performs a correction in the sense of a reduction of the output-determining signal.
The control system represented in the invention can be used with internal combustion engines in the common rail design, the UIS design (unit injector system) or conventional design.